Frequency-domain high-speed bus signal integrity compliance model

ABSTRACT

Embodiments of the present disclosure provide methods for using a compliance model to determine compatibility of a channel with a bus&#39;s chip I/O circuitry at its ends. The method includes identifying at least one design criteria and obtaining boundary sets of frequency domain parameters for compliant signal channels known to achieve the design criteria. In certain embodiments, the boundary sets may be derived using a genetic algorithm. The method further includes verifying whether a particular signal channel is compliant by comparing values of frequency domain parameters for the particular channel to one or more of the boundary sets of frequency domain parameters for the known compliant channels.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 14/721,788, filed May 26, 2015. The aforementioned relatedpatent application is herein incorporated by reference in its entirety.

BACKGROUND

Field of the Invention

Embodiments of the present disclosure relate to a communication bus, andmore specifically, to determining bus channel compliance.

Description of Related Art

Computer server systems have many high-speed signal channelsinterconnecting the central processing units to a variety ofinput/output (I/O) chips which communicate with other computer systems,storage systems, network switches, and a large variety of peripherals.The physical implementation of the channel presents many design choices.Such choices include single-ended or differential wiring and thepartitioning of components that may necessitate multiple printed circuitboards (PCBs) with connectors or even cables. Also, the manufacturingchoices are many and include PCB materials, plated through hole (PTH)vias and stubs, trace cross-sections, the wire gauge of cables,connector design, component mounting and density of the traces needed tocomplete the design.

SUMMARY

Certain embodiments of the present disclosure generally provide a methodfor channel compliance testing. The method generally includesidentifying at least one design criteria; obtaining boundary sets offrequency domain parameters for compliant signal channels known toachieve the design criteria; and verifying whether a particular signalchannel is compliant by comparing values of frequency domain parametersfor the particular channel to one or more of the boundary sets offrequency domain parameters for the known compliant channels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example peripheral component interconnect express(PCIe) third generation (Gen3) channel topology.

FIG. 2 illustrates example operations for channel compliance testing, inaccordance with certain embodiments of the present disclosure.

FIG. 3 illustrates example operations for deriving a compliance model,in accordance with certain embodiments of the present disclosure.

FIG. 4 illustrate an example graph of channel differential insertionloss of a communication bus in decibels (dB).

FIG. 5 illustrates an example graph of channel differential insertionloss and a corresponding fitted curve.

FIG. 6 illustrates an example graph for deriving channel signal tocrosstalk ratio.

FIG. 7 illustrates an example channel template used by a geneticalgorithm to generate a compliance model, in accordance with certainembodiments of the present disclosure.

FIG. 8 illustrates a table of example frequency domain compliance modelboundary sets, in accordance with certain embodiments of the presentdisclosure.

FIG. 9 illustrates eye opening margins for a boundary set of thecompliance model of FIG. 8, in accordance with certain embodiments ofthe present disclosure.

DETAILED DESCRIPTION

There are a large number of channel design and manufacturing choices fordevelopment of high-speed busses (e.g., at 16 Gb/s and above). Thus,simulations may be required to determine compliance of a channel forcommunication between components (e.g., transmitter (Tx) and receiver(Rx) circuits). For example, time-domain simulations are commonly usedto determine channel compliance. As used herein, channel compliancegenerally refers to a channel which meets one or more design criteria.Design criteria may vary, depending on a particular application. As anexample, for channels used to communicate between chip components,design criteria may include achieving a desired bit error rate (BER) forspecific Tx and Rx properties (e.g., at a certain bus speed).

In a time-domain simulation, jitter, crosstalk and switching noiseproperties of a specific Tx (e.g., driver) and Rx combination may beused to evaluate the Tx and Rx equalization on a time-domain data bitpattern propagated through the channel. The result of such a simulationis an eye diagram which provides information on the likelihood of errorwhen passing a “1” or “0” bit through the channel. The properties of theeye diagram may be compared against previously set eye marginrequirements to determine if the eye is passing or failing at a specificBER and as a result, determine if the channel is compliant or not.However, determining channel compliance through time domain simulationsmay require a high level of expertise with a specific time-domainsimulation tool that accurately represents the transmitter and receiver.To obtain a low BER millions of bits may be simulated. As a result, thissimulation may take a significant amount of time to generate results.

Moreover, these simulations may have to be repeated for manycombinations of equalization settings which increases the simulationcomplexity. Equalization settings generally refer to Tx and Rxproperties used to effectively correct a signal such that a Rx componentcan more effectively distinguish between a “0” or “1” bit. Differentequalization settings may work better for different channels. Therefore,a channel may be simulated based on a plurality of equalization settingsto determine the channel's compliance.

Thus, simpler and quicker mechanisms to evaluate channel compliance aredesirable. Embodiments of the present disclosure provide a method fordesigning a frequency-domain channel compliance model which may be usedto determine a channel's compliance. As presented above, a compliantchannel is one that meets a pre-defined set of criteria that ensures thefull channel, in operation, achieves specific design criteria (e.g., abit error rate) for specific Tx and Rx properties (e.g., at a certainbus speed). Once the compliance model has been generated for a given setof Tx and Rx properties, the compliance model may be used to determinecompliance of any channel under test for the set of Tx and Rxproperties. That is, it is not required to generate a new compliancemodel each time a channel is tested for compliance for the set of Tx andRx properties.

In certain embodiments, the channel compliance model may be generatedbased on frequency-domain parameters which may affect a data bit patternpassing through a channel. These channel frequency domain parameters mayinclude insertion loss, insertion loss deviation, signal to cross talkratio, and signal to crosstalk ratio deviation.

For example, for given driver and receiver properties, channelsstressing the many combinations of frequency domain parameters todifferent levels may be simulated in the time domain. The results ofthese simulations provide a set of combinations of frequency-domainparameters representing compliant and noncompliant channels. When asufficient number of cases are simulated, a multi-dimensional modelrepresenting a compliant channel space can be produced. In certainembodiments, a genetic algorithm (GA) may be utilized in order to moreefficiently find the bounds of the compliant channel multi-dimensionalmodel.

To determine the bounds of the compliant channel multi-dimensionalmodel, a GA may be provided with a channel template, the physicalproperties of which the GA may vary (e.g., open area wiring length, pinarea wiring length, or impedance of traces). By varying the physicalproperties of the channel template, the GA is given control to affectthe channel's frequency domain parameters. Thus, the GA may create apopulation of channel variations, each having different combinations offrequency domain parameters. For example, each member of this populationmay have a different insertion loss among other frequency domainparameters.

Each channel variation of the population may be simulated in thetime-domain (e.g., which may include sweeping a plurality ofequalization settings) to determine if the channel variation meets aparticular objective. In this case, the objective may include findingfrequency domain parameters that are on a boundary of compliance withone or more design criteria. For each member of the population, afitness function may be calculated by the GA and used to determine howclose the particular member of the population is to meeting theobjective. If the population of channel variations does not meet theobjective, the GA may generate another population of channel variationsbased on the analysis performed on the previous population (e.g., basedon the fitness functions generated for the previous population). Thisiterative process is continued until a sufficient number of boundarysets of frequency domain parameters are found by the GA.

The compliant channel model produced by the GA can be used as analternative to the time-domain eye simulations to determine theviability of a channel under design. As a result, determining channelcompliance can be done quicker with less computing resources, less userexpertise, and with less specialized simulation tools as compared totime-domain eye simulations.

FIG. 1 illustrates a typical channel topology 100 (e.g., peripheralcomponent interconnect (PCIe)-Generation three (Gen3)). The channeltopology 100 includes two cards, the motherboard 102 and the adaptercard 104, connected to each other using a PCIe slot connector 106 (e.g.,PCIe surface mount (SMT) connector). These cards contain the end pointsof the channel such as the root complex 108 connected to a chip 112(e.g., a processor) on the mother board 102 and the end point device 110(e.g., end point device package) connected to another chip 114 on theadapter card 104. Many physical properties of this channel topology cancontribute towards the degradation or improvement of its signalintegrity. For example, the motherboard and adaptor card include wiring(e.g., inner layer wiring 116A and 116B), one or more vias (e.g., vias118A, 118B, 118C, and 118D), a direct current (DC) blocking capacitor120, and connectors (e.g., hybrid land grid array (HLGA) connector 122).The loss properties of the dielectric materials used in the mother board102 or the adaptor card 104 can affect signal attenuation, the spacingand shielding of traces within the different channel components canaffect crosstalk noise coupling properties, and the level of impedancematching implemented can cause channel signaling reflections.

A set of frequency domain parameters may be used to represent thechannel between two components (e.g., Tx at root complex 108 and Rx atend point device 110). As presented above, once a channel compliancemodel is designed using the frequency domain parameters, the compliancemodel may be used to determine compliance of a channel withouttime-domain analysis, as described with respect to FIG. 2.

FIG. 2 illustrates example operations 200 for testing channelcompliance, in accordance with certain embodiments of the presentdisclosure. The operation 200 begin at 202, by identifying at least onedesign criteria. For example, the design criteria may include a desiredbit error rate (BER) for specific Tx and Rx properties. At 204, boundarysets (e.g., a compliance model) of frequency domain parameters forcompliant signal channels known to achieve the design criteria may beobtained. For example, the boundary sets may be obtained from a storagedevice. At 206, a particular signal channel (e.g., a channel under test)may be verified for compliance by comparing values of frequency domainparameters for the particular channel to one or more of the boundarysets of frequency domain parameters for the known compliant channels.

FIG. 3 illustrates example operation 300 for deriving the boundary sets,in accordance with certain embodiments of the present disclosure. Theoperation 300 begin at 302, by identifying at least one design criteria.As presented above, the design criteria may include a desired BER forspecific Tx and Rx properties. At 304, boundary sets of frequency domainparameters for compliant signal channels known to achieve the designcriteria may be determined. For example, as presented above, theboundary sets may be determined using a GA. The boundary sets are usedfor verifying whether a particular signal channel is compliant bycomparing values of frequency domain parameters for the particularchannel to one or more of the boundary sets of frequency domainparameters for the known compliant channels.

The process of deriving the boundary sets based on frequency domainparameters is described in more detail with respect to FIGS. 4-9. Thechannel frequency domain parameters which may be used to design thecompliance model may include at least one of channel insertion loss atbus fundamental frequency (ILF), channel insertion loss deviation (ILD)measure, channel maximum insertion loss deviation below and above busfundamental frequency (ILDB/ILDA), channel signal to crosstalk ratio atbus fundamental frequency (SXTF), channel minimum insertion lossdeviation below and above bus fundamental frequency (SXTB/SXTA). Valuesfor the frequency domain parameters may be determined based onS-parameters indicative of a frequency response of the particularchannel.

In certain embodiments, the channel ILF parameter may be calculated at afundamental frequency of a bus (e.g., a typical PCIe-Gen3 bus (e.g., 4GHz) in dB). This parameter generally describes the attenuation of asignal travelling through the channel. Its value may be affected inlarge part by dielectric material loss properties, signal propagationdistance and channel impedance matching properties. FIG. 4 illustrates agraph 400 of the insertion loss in dB as a function of frequency. Asillustrated, ILF is measured at the fundamental frequency of the bus(e.g. at 4 GHz).

Channel ILD measure may be used to quantify the amount of reflectionswithin a channel among other things. In order to quantify ILD, a fit ofthe insertion loss curve is generated between 0 Hz and a high frequencypoint defined at which the insertion loss is 40 dB or the highestfrequency in the S-parameter model, whichever comes first. The curvefitting of the insertion loss may be done by moving average smoothing.The moving average smoothing procedure may use a window size of 51discrete frequency points centered at the point under consideration.This window may span a 1.02 GHz range with a 20 MHz step S-parametermodel. While the window size of 51 is provided as an example tofacilitate understanding, different window sizes may be considered if,for example, a different S-parameter frequency resolution is used.

FIG. 5 is a graph 500 of an example insertion loss curve 502 along witha corresponding fitted curve 504 (e.g., moving average smoothing). Oncethe fitted line is obtained, the error between the original insertionloss curve and the fitted curve may be found at each discrete frequencypoint in the S-parameter model. The square of each discrete frequencypoint error may then be found after which the sum of all squares may becalculated and divided by the total number of discrete frequency pointsconsidered. The resulting value is the insertion loss deviation measure.Graph 506 is a zoomed in view of graph 500 which more clearlydemonstration the insertion loss curve 502 and fitted curve 504.

In addition to the ILD measure, ILDB and ILDA parameters are found byfinding the maximum difference between the insertion loss curve and itsfitted curve. ILDB and ILDA may be used because the ILD measure may nottake into account where a deviation happens with respect to frequency.Ripples in the insertion loss at lower frequencies may have a greatereffect on the channel signaling than at higher frequencies. This may bedue to the fact that a channel may have higher transmission amplitudesat the lower frequency. By considering the ILDB and ILDA parameters,worst case frequency dependence may be covered.

The SXTF parameter may be found in order to get a measure of the amountcrosstalk noise on a victim net in the channel under consideration atthe fundamental frequency. This value may be calculated by finding thedifference between the insertion loss and the crosstalk aggression powersum at the fundamental frequency of the bus (e.g., 4 GHz). The crosstalkpower sum from all the crosstalk aggressors may be calculated using rootsum square (RSS).

FIG. 6 is a graph 600 that shows an example signal to crosstalk ratiomeasure at a fundamental frequency of a bus, in accordance with certainembodiments of the present disclosure. The graph illustrates theinsertion loss 602 and the cross talk aggression power sum 604 in dB asa function of frequency. The SXTF may be calculated by measuring thedifference between the insertion loss 602 and the cross talk aggressionpower sum 604 at a fundamental frequency (e.g., 4 GHz), which is 18.35dB in this case.

For SXTB and SXTA parameters, two signal to crosstalk ratio measures areconsidered that are motivated by the fact that crosstalk aggression atfundamental frequency may not be able to solely represent the effect ofcrosstalk on a channel's signaling. The full frequency band of thechannel may be considered. These two measures are the minimum signal tocrosstalk ratio between 0 Hz and bus fundamental frequency and theminimum signal to crosstalk ratio between fundamental and the highfrequency point. The high frequency point may be the frequency at whichthe insertion loss is 40 dB or the highest frequency in the S-parametermodel, which ever point comes first. All discrete frequency pointswithin these frequency ranges may be considered.

In generating the compliance model, channels stressing differentcombinations of the frequency domain parameters described above may besimulated in the time domain given specific driver (or transmitter) andreceiver properties. For example, the driver properties may include slewrate, driver signal level, random jitter, sinusoidal jitter, duty cycledistortion, number of feed-forward equalization (FFE) taps, resolutionof FFE taps, and the number of FFE precursors. Receiver simulationproperties may include random jitter, sinusoidal jitter, automatic gaincontrol (AGC), maximum AGC gain, target level for AGC gain, minimum AGCgain, minimum latch overdrive, AGC gain Gaussian amplitude noise range,number of decision feedback equalization (DFE) taps, and continuous timelinear equalization (CTLE).

The goal of these simulations is to find sets of frequency domainparameter combinations defining the boundaries of a multi-dimensionalcompliance model. To avoid brute force simulations, genetic algorithm(GA) optimization may be used in order to intelligently find boundarysets of the frequency domain compliance model, as described above. Eachset of frequency domain parameters is representative of a boundarycompliant channel.

As presented above, in order to provide the GA with sufficientvariations to produce rich populations of boundary sets, an examplechannel template may be used to represent a channel topology for which acompliance model is to be generated. FIG. 7 is an example channeltemplate representative of a typical PCIe-Gen3 bus, which is adifferentially wired bus, and includes models for the differentcomponents shown in FIG. 7 and described above with respect to FIG. 1.The components include up to eight crosstalk differential aggressors (upto 8 aggressors). Certain channel characteristics were varied resultingin different sets of frequency domain parameters.

Different channel characteristics may be varied by the GA, which includethe length of the pin area wiring 702 and the open area wiring length704 and impedance. All other sections of the channel may be leftunchanged for the all the channel variations exercised by the GA. Incertain embodiments, the pin area wiring length 702 may be varied in 1.1inch segments between 1.1 inches and 8.8 inches total. In addition tobeing a source of signal attenuation, the pin area wiring length may bea source of crosstalk because of the nature of the routing environmentwhich does not allow designers to escape wiring while having enoughseparation between differential pairs or clearance from anti-pads tocontrol crosstalk noise coupling within a layer and between layers. Thecoupling between layers may be increased due to the functionalmisregistration which may be included in the pin area wiring models.

In certain embodiments, the open area wiring length 704 may be varied in2 inch segments between 2 inches and 12 inches total, for example. Eachsegment could be selected to have a differential impedance between 70Ohms and 100 Ohms in steps of 5 Ohms. The open area length 704 may haveminimal crosstalk contribution on the channel because the pairs may besufficiently spaced from each other. The different options available forthe open area wiring could affect signal attenuation and cause channelinternal reflections which results in increased insertion lossdeviation. Of course, in good design practice a constant open areadifferential wiring 85 Ohm impedance would be maintained within themanufacturing process capability. To find the frequency domaincompliance multidimensional model the impedance variation in the openarea wiring is stressed to bound the insertion loss deviation.

Given Tx (e.g., driver) and Rx input/output (I/O) circuit properties,example GA optimization steps which may be used to generate thecompliance model are as follows. First, channel variations (e.g., 100channel variations) may be created using combinations of the channelcharacteristics. For example, this may be performed at random at thebeginning of the first optimization iteration and through the GA'scrossover and mutation operations in following iterations. Each channelvariation may be simulated in the time domain by sweeping a plurality ofequalization settings (e.g., sweeping 80 equalization setting includingFFE and CTLE combinations). The eye results as a result of equalizationsetting sweep for each channel variation may then be processed and thefitness measure for each channel variation may be evaluated. A channelsatisfies a fitness criteria (e.g., has frequency domain parameters thatfall on a boundary of channel compliance) if the channel has only twoequalization settings (of the total 80 swept, for example) that resultin passing vertical and horizontal eye margins. Minimum passing verticaland horizontal eye margins may be 60 mVpp and 15% unit interval (UI) ata BER of 10⁻¹² respectively (e.g., for a custom PCIe-Gen3 bus).

If a certain channel variation is found to satisfy the fitness function,the channel variation characteristics may be saved. All consideredchannel variations may be removed from pool of consideration for thefollowing iterations. Then, the algorithm continues to the nextiteration generating a new population based on what was learned from theprevious iteration of the algorithm.

If no channel variation was found to satisfy the fitness function, thealgorithm continues to the next iteration generating a new populationbased on what was learned from the previous iteration. All consideredchannel variations are removed from pool of consideration for thefollowing iterations. The genetic algorithm continues to run until asufficient number of channel variations satisfying the fitness criteriaare found in order to sufficiently describe the boundaries of thefrequency domain compliance model.

FIG. 8 is a table 800 showing a plurality of example frequency domainparameters representing instances lying on the boundary of themultidimensional frequency domain compliance model obtained as a resultof the operations described above. Each set describes a single boundarycompliant channel. In certain embodiments, given a channel to be testedfor compliance, if at least a single boundary parameter set (e.g.,boundary parameters of index 28) presented in FIG. 8 is found to beworse than the channel under test, then the channel is renderedcompliant. As illustrated, each boundary parameter set is represented byan index number. A worse boundary parameter set would have larger ILF,ILD, ILDB and ILDA but smaller SXTF, SXTB and SXTA. The more frequencydomain sets found by the GA, the more covering the frequency domaincompliance model is.

The “satisfy all” row in the Table V represents a single frequencydomain parameter set obtained by going through all 30 boundary sets andusing the best of each of the seven frequency domain parameters. A testchannel better than the “satisfy all” row would be identified as acompliant channel. However, as can be expected using the “satisfy all”row as a lone frequency domain parameter set to check for compliancewould result in a very restrictive compliance model. This is becausecertain frequency domain parameters in a given channel may be stressedif other frequency domain parameters have better values (for example anincreased loss in a certain channel may still render a channel compliantif it had a large Signal to Crosstalk ratio). Therefore, a channel thatmeets the requirements of any of the index rows may be considered as acompliant channel.

FIG. 9 is a table 900 illustrating the eye opening margins at 10⁻¹² BERfor the parameter set index 28 shown in the table of FIG. 8 afterrunning time domain simulations using the same Tx and Rx properties usedto generate the table of FIG. 8. As presented above, the requiredvertical eye (VEYE) and horizontal eye (HEYE) margins for an examplecustom PCIe-Gen3 bus may be 60 mVpp and 15% UI at a BER of 10⁻¹²respectively. As illustrated, frequency domain parameter set 28 has onlytwo passing eye margins as a result of sweeping all the 80 FFE-CTLEequalization setting combinations (e.g., at preset 7 representing a typeof equalization setting and CTLE 6 and 7 for the horizontal and verticaleye margins). This indicates that the frequency domain parameter valuesof index 28 fall on a boundary of acceptable parameters for a compliantchannel, based on a design criteria of 10⁻¹² BER given the assumed Txand Rx circuit properties to generate the compliance model. Thus, theeye opening margins illustrated in FIG. 9 illustrate that the boundaryparameters at parameter set index 28 satisfy the fitness criteria usedby the GA for defining a boundary case.

The descriptions of the various embodiments of the present disclosurehave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

As will be appreciated by one skilled in the art, embodiments of thepresent disclosure may be embodied as a system, method or computerprogram product. Accordingly, embodiments of the present disclosure maytake the form of an entirely hardware embodiment, an entirely softwareembodiment (including firmware, resident software, micro-code, etc.) oran embodiment combining software and hardware embodiments that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, embodiments of the present disclosure may take the form ofa computer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for embodiments of thepresent disclosure may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Embodiments of the present disclosure are described below with referenceto flowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of thedisclosure. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The present disclosure may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out embodiments ofthe present disclosure.

The computer storage medium can be a tangible device that can retain andstore instructions for use by an instruction execution device. Thecomputer readable storage medium may be, for example, but is not limitedto, an electronic storage device, a magnetic storage device, an opticalstorage device, an electromagnetic storage device, a semiconductorstorage device, or any suitable combination of the foregoing. Anon-exhaustive list of more specific examples of the computer readablestorage medium includes the following: a portable computer diskette, ahard disk, a random access memory (RAM), a read-only memory (ROM), anerasable programmable read-only memory (EPROM or Flash memory), a staticrandom access memory (SRAM), a portable compact disc read-only memory(CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk,a mechanically encoded device such as punch-cards or raised structuresin a groove having instructions recorded thereon, and any suitablecombination of the foregoing. A computer readable storage medium, asused herein, is not to be construed as being transitory signals per se,such as radio waves or other freely propagating electromagnetic waves,electromagnetic waves propagating through a waveguide or othertransmission media (e.g., light pulses passing through a fiber-opticcable), or electrical signals transmitted through a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present disclosure may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Java, Smalltalk, C++ or the like,and conventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform embodiments of the present disclosure.

Embodiments of the present disclosure are described herein withreference to flowchart illustrations and/or block diagrams of methods,apparatus (systems), and computer program products according toembodiments of the disclosure. It will be understood that each block ofthe flowchart illustrations and/or block diagrams, and combinations ofblocks in the flowchart illustrations and/or block diagrams, can beimplemented by computer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implementembodiments of the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present disclosure. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

While the foregoing is directed to embodiments of the presentdisclosure, other and further embodiments of the disclosure may bedevised without departing from the basic scope thereof, and the scopethereof is determined by the claims that follow.

What is claimed is:
 1. A method for channel compliance testing,comprising: identifying at least one design criteria; obtaining boundarysets of frequency domain parameters for compliant signal channels knownto achieve the design criteria; and verifying whether a particularsignal channel is compliant by comparing values of frequency domainparameters for the particular channel to one or more of the boundarysets of frequency domain parameters for the known compliant channels,wherein the signal channel is part of a communication bus and theboundary sets of frequency domain parameters comprise at least oneparameter related to insertion loss and at least one parameter relatedto a crosstalk ratio at a fundamental frequency of the bus.
 2. Themethod of claim 1, further comprising deriving the frequency domainparameters for the particular channel from S-parameters indicative of afrequency response of the particular channel.
 3. The method of claim 1,wherein the design criteria comprises a desired bit error rate for aparticular set of bus transmitter and receiver properties.
 4. The methodof claim 1, further comprising determining the boundary sets using agenetic algorithm.
 5. The method of claim 1, wherein the particularsignal channel is used for communication between a first and secondcomponents and the boundary sets are determined for at least one knownproperty of the first and second components.
 6. The method of claim 1,wherein the verifying comprises: determining whether the particularsignal channel is compliant based on a comparison of the frequencydomain parameters for the particular channel to frequency domainparameters of a first boundary set; and if not, determining whether theparticular signal channel is compliant based on a comparison of thefrequency domain parameters for the particular channel to frequencydomain parameters of a second boundary set.